Hi there,
I've been asking Squarespace this same question for years.
When I signed up I knew that Portfolio posts were the best way to display photographs but saw there was no draft option. I asked the help centre about it as I signed up and was told this may be implemented in the future.
I moved my site from Wordpress to Squarespace because images are displayed so much better here. I even created a Squarespace site for my work. It baffles me that even wordpress had the option to create a draft before going live.
Without the draft option, my posts are rushed and the text is minimal. I'd have many more posts if I had time to work on a post without it being live.
This is the only reason why I don't recommend Squarespace to others.
Please help me out